216 Francois Vurpillot et al.
Figure 6. Comparison of secondary ion mass spectrometric (SIMS), atom probe tomography (AP), and field-ion microscopy (FIM) brightness depth concentration profiles through the boron δ layers in the boron–silicon multilayer sample.
into a calibrated depth profile using a depth increment/ image value of 0.0135 nm/image, which is derived from the known silicon thicknesses between each δ layers. The final concentration profile is displayed in Figure 6, together with a secondary ion mass spectrometric (SIMS) spectrum (measured with an O2
The brightness profile across the layers is transformed
250 eV), and APT results. The SIMS concentration profile displays a strongly degraded depth resolution. This is due to the roughness of the 100nm Si cap, which has a root mean square roughness of 3.9nm as measured using atomic force microscopy. The latter propagates through the entire analysis and degrades the depth resolution. Qualitatively this figure shows that the concentration profile obtained from the FIM data is in good agreement with the SIMS and APT profiles. The good match of the depth location of the different boron peaks indicates that the sample was analyzed using a constant field-evaporation rate. The best resolution is achieved using FIM, probably because FIM is less affected by trajectory effects close to the protruding B layers at the specimen’s surface (Vurpillot et al., 2009). For the APT measurements, the depth resolution
+ beam with an ion energy impact of
achieved for the boron δ layers is known to be degraded because of field-evaporation differences between Si and B, which can possibly lead to local magnification effects, trajectory overlaps, laser-induced specimen asymmetries, and atom migration (Gault et al., 2012; Larson et al., 2013).
Dislocation Loops
FIM imaging of boron in silicon, demonstrated in the δ layer research, shows that more complex structures that cannot be readily revealed in detail with other techniques can be investigated. In silicon with a smaller concentration of B, FIM allows us to image the boron atoms in parallel with the underlying silicon crystal. This ability makes it possible to
Figure 7. Demonstration of atomic-scale imaging using field-ion microscopy (FIM) on a silicon specimen oriented along a <110> direction. Image shows silicon (111) planes as imaged by FIM. The FIM micrographs display a high regularity of the atomic positions within each plane. Boron atoms are imaged with a very high brightness.
image directly the positions of boron atoms with respect to crystal defects. A boron-implanted and thermally annealed silicon
sample was investigated using FIM to reveal the 3D dis- tribution of boron atoms in the silicon crystal. The presence of the boron-decorated dislocation loops has been postulated in such samples because TEM images clearly show defect loops after the annealing step and, concomitantly, electrical measurements exhibit a decrease in the electrical activation of the dopants, and therefore incorporation of boron in the silicon lattice is diminished. No direct observation of such segregation has been provided until now. Using FIM, the crystallographic planes of the silicon lattice, as well as the position and orientation of the defect plane, can be imaged simultaneously with the accumulation of boron atoms decorating this defect plane (Figure 7; Koelling et al., 2013). The concurrent identification and localization of boron clusters and crystal defects makes it possible to characterize completely the formation and dissolution of boron clusters in silicon on the atomic scale. The FIM approach is more sensitive than alternative techniques, revealing about twice as many boron-decorated loops per unit volume as defects observed utilizing TEM and about 10 times as many loop-like boron structures as we detected employing APT measurements on the same sample. The higher sensitivity of FIM makes it possible to employ smaller implantation doses in addition to imaging a wider range of defects. Careful examination of the FIM micrographs demonstrates (1) that the habit planes of dopant-decorated defects are more diverse when compared with the presently accepted dom- inance of (111) defects; and (2) that boron segregation along the edges of the dislocation loops varies and that individual positions along the edges are not decorated with single boron atoms, but with boron clusters with a subnanometer diameter. This detailed atomic-scale information on the structure of boron loops represents the basis for refining existing theories describing defect-dopant dynamics.
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85 |
Page 86 |
Page 87 |
Page 88 |
Page 89 |
Page 90 |
Page 91 |
Page 92 |
Page 93 |
Page 94 |
Page 95 |
Page 96 |
Page 97 |
Page 98 |
Page 99 |
Page 100 |
Page 101 |
Page 102 |
Page 103 |
Page 104 |
Page 105 |
Page 106 |
Page 107 |
Page 108 |
Page 109 |
Page 110 |
Page 111 |
Page 112 |
Page 113 |
Page 114 |
Page 115 |
Page 116 |
Page 117 |
Page 118 |
Page 119 |
Page 120 |
Page 121 |
Page 122 |
Page 123 |
Page 124 |
Page 125 |
Page 126 |
Page 127 |
Page 128 |
Page 129 |
Page 130 |
Page 131 |
Page 132 |
Page 133 |
Page 134 |
Page 135 |
Page 136 |
Page 137 |
Page 138 |
Page 139 |
Page 140 |
Page 141 |
Page 142 |
Page 143 |
Page 144 |
Page 145 |
Page 146 |
Page 147 |
Page 148 |
Page 149 |
Page 150 |
Page 151 |
Page 152 |
Page 153 |
Page 154 |
Page 155 |
Page 156 |
Page 157 |
Page 158 |
Page 159 |
Page 160 |
Page 161 |
Page 162 |
Page 163 |
Page 164 |
Page 165 |
Page 166 |
Page 167 |
Page 168 |
Page 169 |
Page 170 |
Page 171 |
Page 172 |
Page 173 |
Page 174 |
Page 175 |
Page 176 |
Page 177 |
Page 178 |
Page 179 |
Page 180 |
Page 181 |
Page 182 |
Page 183 |
Page 184 |
Page 185 |
Page 186 |
Page 187 |
Page 188 |
Page 189 |
Page 190 |
Page 191 |
Page 192 |
Page 193 |
Page 194 |
Page 195 |
Page 196 |
Page 197 |
Page 198 |
Page 199 |
Page 200 |
Page 201 |
Page 202 |
Page 203 |
Page 204 |
Page 205 |
Page 206 |
Page 207 |
Page 208 |
Page 209 |
Page 210 |
Page 211 |
Page 212 |
Page 213 |
Page 214 |
Page 215 |
Page 216 |
Page 217 |
Page 218 |
Page 219 |
Page 220 |
Page 221 |
Page 222 |
Page 223 |
Page 224 |
Page 225 |
Page 226 |
Page 227 |
Page 228 |
Page 229 |
Page 230 |
Page 231 |
Page 232 |
Page 233 |
Page 234 |
Page 235 |
Page 236 |
Page 237 |
Page 238 |
Page 239 |
Page 240 |
Page 241 |
Page 242 |
Page 243 |
Page 244 |
Page 245 |
Page 246 |
Page 247 |
Page 248 |
Page 249 |
Page 250 |
Page 251 |
Page 252 |
Page 253 |
Page 254 |
Page 255 |
Page 256 |
Page 257 |
Page 258 |
Page 259 |
Page 260 |
Page 261 |
Page 262 |
Page 263 |
Page 264 |
Page 265 |
Page 266 |
Page 267 |
Page 268 |
Page 269 |
Page 270 |
Page 271 |
Page 272 |
Page 273 |
Page 274 |
Page 275 |
Page 276 |
Page 277 |
Page 278 |
Page 279 |
Page 280 |
Page 281 |
Page 282 |
Page 283 |
Page 284
